Method and apparatus for prediction and warning of hypoglycaemic attack

ABSTRACT

A method and device for warning diabetics of imminent hypoglycaemic attacks. EEG signals are collected from a person using subcutaneously placed electrodes and the signals are led via wires drawn under the person&#39;s skin to a subcutaneously placed signal interface unit from where they are transmitted to an externally worn signal processing unit. The signal processing analyzes the EEG signals and when the pre-seizure characteristics signal changes are detected, a warning signal is given to the person from an alarm giver built into the signal processing unit, e.g., in form of a vibrator. When a person detects a warning signal, the person can prevent the hypoglycaemic attack by, e.g., consuming a sugary food.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 11/793,271 filedFeb. 19, 2008, which is the national stage of PCT/DK2005/000739 filedNov. 21, 2005, which claims priority from Danish Application PA200401955dated Dec. 20, 2004, the disclosures of which are incorporated in theirentirety herein.

BACKGROUND OF THE INVENTION

The invention relates to a method of predicting and warning ofhypoglycaemic attacks for people such as diabetics.

Moreover the invention relates a device for prediction and warning ofhypoglycaemic attacks for people such as diabetics.

Hypoglycaemic attacks occur as a result of too low a blood sugarconcentration, which is mostly a problem for diabetics, who are treatedwith insulin or other blood sugar regulating medical drugs.

The attacks can be highly severe and often entail unconsciousness.

The risk of an attack therefore often limits the possible activities ofthe people, which furthermore decreases the quality of life for thesepeople.

Attacks can be prevented in a simple way if the people e.g. consumeappropriate food when the glucose values become critical.

The problem is however that many in the risk group cannot by themselvesfeel when the blood sugar concentration reaches a critically low levelwith risk of an attack.

The number of people in the risk group is approximately 1 million.

There are known methods and devices for prediction of hypoglycaemicattacks.

In U.S. Pat. No. 6,572,542 a method and a device are described, whichamong others have the purpose of warning of hypoglycaemic attacks. Theknown technique primarily uses registration of changes in a person's ECG(electrocardiographic) signals as a result of a critically low level ofblood sugar, to emit a signal of warning. The changes in the ECG signalsare in an example described in the patent specification linked with EEG(electroencephalographic) signals from the person in order to clarifythe blood sugar dependent changes in the ECG signal.

It has been found, however, that this prior art involves some drawbacks.

Since the technique requires signal analysis of both the ECG and EEGsignals from the person on whom the measurements are being taken, thealgorithms for calculating become relatively complex, which specifieshigh demands for hardware processing power and at the same time demandsa high power draw.

If this is linked together with the fact that a relatively high numberof electrodes for both ECG and EEG signal collection are necessary, itresults in a relatively big and complex product, which is difficult toapply in the daily life of a person.

It is furthermore generally known that the greater complexity a productcontains, the greater is the risk that the product will become unstable.

The mentioned drawbacks have overall meant that the hitherto knowntechnique has not resulted in the manufacturing of products, which canenhance the quality of life for wide parts of the risk group.

SUMMARY OF THE INVENTION

It is therefore a purpose of the invention to improve the known methodand the known device. The object of the invention is achieved by amethod for warning of hypoglycaemic attacks, which is characterized inthat the warning is based on analysis of one or more EEG signals fromthe person.

Hereby, it is thus possible to reduce the number of electrodes, sincethe ECG signal is not going to be used, simultaneously the complexity isreduced, and the demands for processing power and the need for powerdraw is also reduced.

In this way it is possible to manufacture a simple, robust and highlyportable alarm system, which basically everyone in the seizure riskgroup can have advantage of It is furthermore a preferred feature of theinvention that the warning is given after signal analytic identificationof pre-seizure characteristic EEG changes such as decrease in frequencyand increase in amplitude.

Tests have shown that the EEG signal changes in a simple andcharacteristic way in the time leading to a hypoglycaemic attack. Asignal analytic identification of the characteristic changes in thefrequency and amplitude has shown to be a good, safe and robust basisfor release of an alarm signal.

The alarm signal can be released in sufficient time before a seizure istriggered, so that the person can easily have time to prevent an attack.

It is furthermore a preferred characteristic of the invention that theEEG signals are registered from two or more electrodes placedintracranially or extracranially on the skin surface or subcutaneously.By placing the EEG electrodes outside the skin the electrode to skincontact impedance and thus the signal detection will vary with e.g. themoisture of the skin and the head movement of the patient. If theelectrodes are placed subcutaneously the location will be permanent andthe electro impedance more stable, which makes the whole warning systemmore robust.

It is furthermore a preferred characteristic of the invention that theEEG signals from the electrodes are transmitted via subcutaneously drawnwires to a subcutaneous placed signal interface unit orsignal-processing and alarm unit.

With these characteristics it is among other things made possible tomanufacture a warning system for hypoglycaemic attacks, which is notvisible, since the whole unit can be placed subcutaneously.

Further preferred embodiments of the method of the invention aredescribed below

As mentioned the invention also relates to a device.

This is characterized in that the device collects EEG signals from twoor more electrodes and by signal analysis identifies pre-seizurecharacteristic changes in the EEG signal such as declining frequencycontent and increasing amplitude and after identification of thecharacteristic EEG changes delivers a warning signal.

The device thereby becomes simple, robust and highly portable.

Further preferred embodiments of the device are also described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be explained more fully with reference to thedrawings, in which:

FIG. 1 shows an example of EEG signal sequences with both normal signalsand the pre-seizure characteristic changes.

FIG. 2 shows a person with a subcutaneously placed hypoglycaemic seizurewarning system.

FIG. 3 shows a block diagram of the warning system from FIG. 2.

FIG. 4 shows a person with a warning system, which is partlysubcutaneously placed and is partly external.

FIG. 5 shows a block diagram of the warning system shown in FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1 is shown part of four EEG signals derived from a person inadvance of a hypoglycaemic attack. The four signals, which originatefrom different electrodes placed on the person's head skin, have beengiven the numbers 1 through 4.

The EEG signals are drawn in a co-ordinate system with indication oftime on the horizontal axis and the signal amplitude on the verticalaxis.

The time sequence specified with 5 shows a normal process of the EEGsignals, while the time sequence specified with 6 shows the EEG signalin advance of a hypoglycaemic attack.

In the normal time phase 5 the EEG signals as shown with 7 arecharacterized in that they oscillate with a given mean frequency andwith a given mean amplitude, which is comparable for all the four shownEEG signal derivations. In the pre-seizure time phase 6 it is clearlyseen, as indicated with 8, that the EEG signal in this phase is changedboth significantly and characteristically. The wavelength of the signalbecomes notably increased, similar to a comparable frequency reduction,concurrent with the signal amplitude being strongly increased.

The listed characteristic changes in the EEG signals in the pre-seizurephase often occur several minutes before a hypoglycaemic attack istriggered. Hereby there is sufficient time to give an early warning tothe person on the basis of the detected EEG signal changes. The personcan then prevent the seizure, e.g. by consuming a sugary food product.

As it appears from FIG. 1 there are relatively notable changes in theEEG signal in the phase in advance of a hypoglycaemic attack. For thesame reason it is relatively simple to detect these changes by the useof appropriate signal analysis algorithms.

The signal analysis can be performed in both the time- and frequencydomain and can be based on more in other applications well-provenalgorithms such as e.g. Bayes' methods, logistic regression or neuralnetworks. Tests have shown that algorithms based on Bayes' methods,including Bayesian classifier has been especially appropriate in orderto, with high precision, detect the pre-seizure characteristic changesin the EEG signals.

It can be appropriate to build in dynamics in the signal processingalgorithms in such a way that these are continuously adapted to thesingle person, who is going to be warned. Such a dynamic adaptation ofthe warning algorithms is a part of the present invention. In order toachieve the best possible result of the signal processing it isappropriate to pre-filter the EEG signals including e.g. by band-passfiltering these, in order to eliminate noise from other signal sourcesin the highest possible extent.

Regarding signal analysis, it is always aimed for to get the bestpossible signal/noise ratio. It will therefore be optimal to place thesignal electrodes directly in the brain, from where the signal activity,which it is desired to measure, originates.

Tests have shown that recording of the blood sugar concentration occursin the brain's hypothalamus area.

It is thus a part of the present invention to place electrodes directlyin the hypothalamus area in order to achieve the best possiblesignal/noise ratio on signals for warning of hypoglycaemic attacks.

FIG. 2 shows a person 9 provided with a warning system in accordance tothe invention. Subcutaneously placed electrodes 10 record the EEGsignals, which via wires 11, drawn under the skin, are lead to a signalprocessing unit 12, which is also placed below the skin.

The signal processing unit 12 processes via the implemented signalprocessing algorithms the measured EEG signals, and when the previouslymentioned pre-seizure characteristic changes in the signals aredetected, the unit 12 delivers a warning signal to the person 9.

The unit 12 is in FIG. 2 shown placed in the person's upper chestregion, but can obviously also be placed a random place, e.g. behind theneck or where it seems the most appropriate for the single individual. Ablock diagram for the system shown in FIG. 2 appears in FIG. 3.

Since the unit 12 is placed below the skin the alarm to the person cane.g. be delivered via a vibrator 14 integrated in the unit 12.

In FIG. 3 is shown 3 EEG electrodes from where the signals are lead tothe signal processing unit 12. In practice any number of electrodes fromtwo and more can be used, and the shown number is therefore not anylimitation of the invention.

Even though the system in terms of signal is designed in order toachieve as high a signal/noise ratio as possible, there can probablyarise situations where loud noise from the environment will reduce thepossibility of sufficiently detecting the characteristic pre-seizurechanges in the EEG signals.

In such a situation the system unit 12 can be programmed to deliver awarning signal to the person 9, which indicates that the seizuresurveillance efficiency is lowered because of external noise. Such awarning signal, which must be separable from the normal pre-attackwarning signal, can help the person, if possible, to remove or reducethe external noise source.

By differentiating the signal giver, e.g. by giving each signal aparticular vibration frequency, several types of alarm- or informationsignals can be delivered, e.g. about the charging state of the energysupply.

The unit 12 must in order to function optimally be provided withelectronics for adaptation of impedance for the electrodes and signalboosters and means for digitization of the analogue EEG signals. Thedigitized signals are subsequently processed in a calculation circuitsuch as a digital signal processor. The unit 12 can be provided with abattery for energy supply.

The service life of the battery obviously depends of the choice of theelectronic components, which are a part of the unit 12.

With present-day technique a service life of several years will beachievable. The service life and the size of the product will, however,to a certain extent always be proportional.

In those cases where e.g. the product's size is of decisive importance,it can be an advantage to split the system into a part, which is placedunder the patient's skin and which only demands a minimum of power andan external part, which demands more power.

A warning system, which consists of an internally placed part below thepatient's skin and an external part, is shown in FIG. 4.

In a system as shown in FIG. 4, the internal unit 12 can solely consistof an interface unit with a low power draw, which gathers the EEG signalfrom the electrodes and transmits them wirelessly through the skin to anexternal unit 13, which can e.g. be placed in the breast pocket of ashirt.

A block diagram of the system shown in FIG. 4 is seen in FIG. 5.

The unit 13 can in this example contain the more power demandingcomponents, including the signal processing unit and the alarm signalgiver 14, and electronics for wireless communication with the unit 12,which is placed under the skin.

When the signal giver is externally placed, the alarm, which isdelivered from 14, can e.g. be an acoustic warning device as analternative to a vibrator.

It is also possible to have a configuration like the one shown in FIG.4, where the unit 12 is the complete unit with integrated signalprocessor and alarm giver, and where 13 in the principle is just abattery charging circuit, which wirelessly through the skin can chargethe batteries in the unit 12. Such a battery charging can be produced onthe basis of known techniques for wireless charging of batteries, e.g.through magnetic interaction of spools in respectively thecharger/sender 13 and the receiver 12, which is going to be charged.

In case the unit 12 is provided with a signal processor, it will oftenbe appropriate to provide the unit 12 with a communication circuit sothat the signal processing program can wirelessly be updated from anexternal computer unit. With the application of a wireless communicationcircuit, it will at the same time be possible to transfer data from theunit 12 to the external unit 13 or one or more substituting externalunits in the form of data collection units or computers.

The present invention covers all combinations of system compositions,which directly or indirectly can be derived from the drawings 2 through5 and the supplemental description to these.

What is claimed:
 1. A method for warning of imminent hypoglycaemicattacks for people such as diabetics, the warning being based onanalysis of one or more Electroencephalography (EEG signals from aperson without the use of Electrocardiography (ECG) signals, said methodcomprising: providing the person with a portable hypoglycaemic attackwarning system comprising EEG signal gathering electrodes and a signalprocessing unit, receiving in said signal processing unit EEG signalsderived from said signal gathering electrodes, performing analysis ofsaid signals for identifying characteristics therein indicative of animminent hypoglycaemic attack by signal analytic identification ofpre-seizure characteristic EEG changes which include at least one ofdecrease in frequency and increase in amplitude, and giving a warning tosaid person that a said attack is determined to be imminent when saidcharacteristics are identified in said EEG signals.
 2. The methodaccording to claim 1, wherein said EEG signals are received first in aninterface unit connected to said electrodes and comprising a wirelesstransmitter, and are wirelessly transmitted by said wireless transmitterof said interface unit to said signal processing unit.
 3. The methodaccording to claim 2, wherein said interface unit is implanted beneaththe skin of the person and said signal processing unit is externallyworn.
 4. The method according to claim 2, wherein the electrodes areconnected to said interface unit by subcutaneously drawn wires and saidinterface unit is subcutaneously placed.
 5. The method according toclaim 1, wherein the EEG signals are registered from two or more saidelectrodes placed intracranially, or placed extracranially on or belowthe skin surface.
 6. The method according to claim 1, wherein the EEGsignals prior to the signal analysis are filtered through band-passfiltering.
 7. The method according to claim 1, wherein the signalanalysis of the EEG signal is carried out in the time domain or in thefrequency domain.
 8. The method according to claim 1, whereinpre-seizure characteristic EEG signal changes are detected byapplication of signal analysis based on a logistic regression algorithm,a Bayesian classifier algorithm, or a neutral network algorithm.
 9. Ahypoglycaemic attack warning device for warning of an imminenthypoglycaemic attacks for people such as diabetics, said devicecomprising: Electroencephalography (EEG signal gathering electrodes anda signal processing unit connected to receive in said signal processingunit EEG signals derived from said signal gathering electrodes in use,said signal processing unit being adapted to perform analysis of saidsignals for identifying characteristics therein indicative of animminent hypoglycaemic attack by signal analytic identification ofpre-seizure characteristic EEG changes which include at least one ofdecrease in frequency and increase in amplitude, and an alarm unitconnected to said signal processing unit and adapted to give a warningthat a said attack is determined to be imminent when saidcharacteristics are identified in said EEG signals.
 10. The deviceaccording to claim 9, further comprising an interface unit physicallyconnected to said electrodes and comprising a wireless transmitter fortransmitting EEG signals received from said electrodes in use, whereinsaid signal processing unit comprises a wireless receiver for receivingsaid transmitted EEG signals for processing.